1. Field of the Invention
The present invention relates to a procedure for marking documents or products, implementing optical markers such as diffraction gratis, such as for example holograms.
2. Description of the Related Art
The use of holograms for the authentication of documents is known in the state of the art. For example, European patent No. EP-79 100 626 describes an identification card with a hologram and also a manufacturing procedure and a method for recording the hologram on the identification card According to this document in the prior art, the identity card carries readable information and at least one hologram containing the readable information, with the hologram being recorded adjacent to other information on a common recording layer. The other information, which is recorded on the common recording layer, is the readable information
Because the implementation of a hologram requires a significant amount of know-how and means that usually are not available to counterfeiters, the security of documents marked in this way is improved.
Another document in the prior art, i.e., Utility Certificate No. FR-92 02 849, discloses a procedure for the marking of bodies (i.e., items) and a device for the identification of bodies marked in accordance with the said procedure,
This procedure is characterized essentially by the fact that it consists of implementing, on a substrate, a first hologram of a first object that is readable under white light, and of implementing on the same substrate a second hologram, known as a "Fourier hologram", of a second object. The second object consists of a plurality of point sources of light, which sources are distributed in a random manner, and further involves bonding the said substrate to the body. The invention also relates to a device that allows the identification of bodies when they have been marked in accordance with the procedure.
Another document in the prior art, i.e., French patent No. FR-2 671 032, as issued to the present applicant, relates to the protection of documents against counterfeiting. This protection relates more particularly to a non-counterfeitable layered document that includes a substrate with a marking region that has two surfaces and that carries information which forms a relief pattern on one of its surfaces and hollows or recesses on its other surface, and that also includes a hologram which carries a holographic interference pattern that covers at least part of the surface of the marking region which carries the information forming hollows or recesses. A layer of adhesive ensures the fixation of the hologram to the marking region.
Another document in the prior art, i.e, European patent No. EP-80 104 962, describes an identity card that contains information in holographic form and that includes a substrate which serves as the basic element of the card. A transparent layer is deposited on the substrate and forms a flat optical waveguide, and another layer is placed on the said waveguide and includes at least one hologram containing a piece of information. The said patent also describes a light-coupling device which consists of another hologram that corresponds to a particular predetermined reference light source, and by means of which only one homologous light wave, which corresponds to the particular reference light source, may be injected by coupling into the waveguide.
Overall, these procedures are satisfactory for securing documents that receive information beforehand, in printed form.
However, the information fiction and the authentification function are completely independent and are implemented in two different regions of the document. The result is the possibility of fraud through the modification of the information present on a document that also carries an authentic marked region.